Casting easily oxidizable metals



Patented July 19, 61 932 v UNITED STATES PATENT OFFICE ROBERT T. WOOD, OF LAKEWOOD, OHIO, ASSIGNOR, BY MESNE ASSIGNMENTS, TO HAG- NESIUM DEVELOPMENT CORPORATION, A

CORPORATION OF DELAWARE CASTING EASILY OXIDIZABLE METALS No Drawing.

This invention relates to the casting of the easily oxidizable metals in molds made of sand or similar agglomerated materials. The invention is particularly directed toward processes and means by which the casting of these metals may be accomplished without the attendant well known difiiculties heretofore encountered. Of the easily oxidizable metals magnesium is commercially the most important.

The propensity of metals of the class mentioned to react violently with moisture and to combine with the oxygen and nitrogen of the atmosphere has been a serious obstacle to their successful casting in sand molds. In

accepted foundry practice for ordinary metals there is usually added to the sand or other similar molding materials a tempering medium, in most cases water, which imparts '20 to the sand the properties necessary to satistive action sufficient to permit the use of factory, molding. It was accordingly supposed that in order to successfully cast magnesium and similar metals in such molds, the mold must be dried by v careful heating in order to prevent attack of moisture on the molten metal.

To overcome the well known diificulties, several methods have been suggested. For example, it has been proposed, in conjunction with the drying method, to incorporate in the molding material a substance which,

when the mold becomes heated, will produce a vapor around the metal to protect it from the atmosphere. Obviously the vapor of such a protective substa'nce'must have little or no effect on the metal. It has also been proposed to use certain protective substances such as sulfur, urea, oxalates, 'or boric acid, which are IBPOItEd f to be usable in an undried sand mold, inthe belief that the vapors given ofl by these substances, when heated, would adequately isolate the metal and protect the same from attack by moisture in the mold. Practice, however, has shown thatv of these substances sulfur alone exerts a protecwater as a tempering-medium if good castings of commerclal size are to be produced. In spite of the numerous investigations which have been undertaken relative to thesive process and the incorporation of a pro- Application filed October 23,1929. Serial No. 401,958.

casting of the easily oxidizable metals in sand molds, the commercial foundry is still faced with difficulties when casting these metals. The drying of the mold is a'tedious, expentective substance has not been found to produce in all instances the desired effect. As stated above, sulfur may be employed to eliminate the necessity of drying the mold; but in this case also, thecastings produced do not represent the optimum in desirable characteristics. I

The chief object of the present invention is to provide an improved method of utilizing the protective idea witheasily oxidizable metals, to enable sound castings to be obtained, in a commercial foundry, of a good color and free, or substantially so, from oxid films and blow holes. Further objects are to provide a method for the production of sounder and cleaner castings of large size than has heretofore been considered possible; to provide new protective substances and molding mixtures containing the same, by which these methods may be carried out; and to modify and adapt some of the. previously known protective substances so as to produce a more eificient protective effect, particularly in molds containing moisture. 1 My invention is developed from and predi-' cated upon an investigation extending over a considerable period of time. In the course of this investigation, in which new and also previously known protective substances were used in both dried and undried sand molds and easily oxidizable metals, notably magnesium and its alloys, were cast therein under varied commercial foundry conditions, I observed that while in the presence of some protective substances excellent castings might be made, there was a tendency for the castings to become less satisfactory as their size was increased. Although this had been previously noted, no method has been heretofore developed for satisfactorily overcoming the difliculty; v I have devised a method by which th1s difiiculty may be overcome and good castlngs' of a very considerable size may be produced. I have, moreover, found that thls method possible the presence, in the mold and produces better results with smaller castings thanhad heretofore, within my knowledge,

been obtained. In its preferred form my por, regardless of the temperature to whichbrought by the hot metal. My

the mold is invention is not, however, limited to a plurality of protective vapors but includes the vapor of an organic borate alone.

Most of the methods heretofore devised for casting magnesium or similar metals in sand or the like required that the protective substances be incorporated in the sand and that the mold made from this mixture be thoroughly dried beforeuse in order to eliminate whatever water was added to or was present in the sand. Of the protectivesub- J stances suggested for use in such dried molds, the-'polyhydric alcoh'ols and specifically glycerin hadv been found to be especially eflica- 'cious. It had been thought, however, that such polyhydric alcohols were eflicient only when used in dried sand molds. I have found that the contrary is true and that when combined with other protective substances, for

example sulfur, annnoniumbisulfate, ammomum fiuorid, naphthalene, and especially boric acid, these alcohols may be used in a moist sand moldv with good results. This leads to important advantages, for in the old-1 er methods of using the polyhydric alcohols the sand was dried before molding and enough of such alcohols was then'added not only to protect the metal but also to lend 'the proper molding qualities to the sand.

Bythe use of the polyhydric alcohols in aqueous' solutions according 'to my invention, the drymg of thesandis rendered unnecessary and the sand is found to have improved-moldmg qualitles as compared to ones using anon-aqueous solution of polyhydric alcohol as the tempering medium. Moreover, amount of the alcohol required is materially reduced since it is no longer necessary-to add more'alcohol than will produce the de-' sired protective effect on. the metal. Al-

5 though glycerin has been mentioned as the desirable polyhydric alcohol for use as 'to glycerin in eflect is produced by the use of a 25 per cent aqueous solution of either ethylene or d1- tective substance, .I have found that when used in aqueous solutions ethylene glycol and di-ethylene glycol are mark that substantially the same Handbook of Organic the p adding to v (preferably about 40 per cent) aquea proedly superior ethylene glycol as can be produced by the use of a 50 per cent solution of glycerin.

- In using aqueous solutions of one of the polyhydric alcohols, such as glycerin and ethylene and diethylene glycol, it was noted that with boric acid also present, results were produced which were superior tothose obtained with molds lacking this particular combination of protective substances. As a result of my investigations I believe this unexpected efl'ect is caused by the presence, in the sand, of what is probably an organic borate, formed by reaction between the polyhydric alcohol and the boric acid at the elevated temperatures to which the mold is brought by the molten metal. Beilsteins pound having the formula '(C H O B) which, it is stated, may be obtained by heating glycerin and boric anhydrid. together.

My experiments indicate that when glycerin and boric acid are present in the sand the compound described by Beilstein, or one much like it, is formed as the mold becomes heated. Possibly the compound produced when ethylene glycol is used has the analogous formula (C H O B) Whatever the actual composition may be, I use the expression organic borate hereinafter to include the compound just referred to and similar compounds, as for example the one listed in Beilstein above and the one formed by reaction between boric acid and diethylene glycol At any rate, by sand a compound adding to the molding formed by the'reaction between boric acid and ethylene or di-ethylene glycol, which is presumably an ethylene borate, or, more gen- Chemistry lists a comerally, an organic borate, I have achieved practically the same results as those obtained with a mixture of boric acid and a polyhydric alcohol. he use of an organlc borate alone, or of boric acid and a polyh'ydric gives a protective effect on magnesium or like metals which is superior to that obtained with any one substance heretofore known to me,

and the castings produced are in uality second only to those obtained in mol scontainin of variant vaporizing temperatures. In using boric acid and a polyhydric alcohol (with consequent formationof an organic borate when the 'metal is poured), I have found that alcohol without other protective substance,

a. plurality of protective substances excellent commercial results can'be obtained by incorporating in the molding sand 1 to 3 per cent (by weight) of boric acid and then the mixture enough of a 25to7 5 per cent p ous solution-of ethylene or di-ethylen'e glycol, to give the desired molding qualities. -In molds formed of such sand I have produced magnesium and magnesium alloy castings of distinctly superior quality, both from the standpoint of soundness and strength and from thestandpoint of color. Other quantities of boric acid and other amounts of .thesame or another polyhydric alcohol may be mixed with the sand and very good results obtained. I have also found that as a substitute for boric acid ammonium borate may be employed; or borax and a mineral acid, say hydrochloric-or sulfuric, which will react with the borax'to produce boric acid. These substitutes will gve, in combination with the polyhydric alcohol, substantially the same results as are obtained with boric acid and the same alcohol.

I In the further course of my investigations I have found other substances, namely potassium sulfid and ammonium bisulfate, which when incorporated in the sand and heated by the molten metal, also exert a protective action sufficient to make possible the production of good castings of the readily oxidizable naphthalene.

metals, and they have, moreover, a protective action even in undried molds. These substances, potassium sulfid and ammonium bisulfate, may be used singly; or either may be used with other protective substances in the same mold. Each of them, when present as the only added: rotective substance, say to the amount of about 2 per cent of the total solids of'the mixture, will make possible the production of castings of limited size in undried sand molds. As between them, ammonium bisulfate is in general preferred. Moreover, either or both of these two substances, the protective properties of which were heretofore unknown, may be used advantageously ,in practicing my described method of pro 'ducing large sized castings by means of a plurality of protective agents.

Other substances, some of them already at least the use 'of this compound, in cmbina-- tion with a resin, has been suggested to overcome the difficulties incident to molding when no water is used as binder. I have. found, however, that naphthalene in amounts of 7 to 10 per cent by weight of the total mix- 1 'ture, exerts a protectlve effect in moist sand which is'in some cases adequate,- especially for magnesium. I have also discovered that similar hydrocarbons, such as anthracene,

chrysene, etc., produce similar results and I consider them to be substantial equivalents of naphthalene. All of 'theabove mentioned protective substances I have used in carrying out my novel method above described. Some are better than others but all, when used with other substances in accordance with my method, produce'an eflect superior to that produced by any one of them singly.

In practicing my improved method in its preferred form, which involves incorporat- 'ing in the molding material a plurality of substances capable of producing a protective vapor, I have devised certain combinations of protective substances of which examples will now be set forth, and have found that in selecting the various protective substances according to theirvaporizing temperatures their boiling points may, in general, be COI1-' 'sidered to be indicative of their relative vaporizing temperatures. Thus ethylene gly- -col has a boiling point of 197 0., naphthalene 218, (Ii-ethylene glycol 250, glycerin 290, sulfur 440, ammonium bisulfate 490. Boric acid volatilizes 'm steam and in polyhydric alcohols. Ammonium fluorid has no true boiling point but it begins to vaporize and dissociate at comparatively low tempera tures. Of ethylene borate it can be said that when the compound is produced by heating ethylene glycol and boric acid in water to simulate the conditions occurring in a sand mold I distillates are obtained from about 120 C. to as high as 280 which upon analysis are found to contain boron and This is probably one reason organic matter. why ethylene glycol and boric acid are so effective when used together. In some cases I prefer to use an organic borate, for example the ethylene borate just mentioned, as at least one of the plurality of protective substances, and sulfur as another, since I have found that moldi'ng mixtures containing the substances named are capable of producing better and larger castings than could heretofore be obtained. However, the presence of both these particular substances is not necessary to produce large sized castings or to produce smaller sized castings of a quality not heretofore obtainable, and in fact in some cases a combination containing only protective substances which were well known before my present invention, produces results superior to any which were theretofore obtained. Among substances usable alone, organic borate, sulfur, naphthalene, and ammonium bisulfate are especially effective, and one or more, of these substances are included in each of the mixtures outlined be- I low, but the invention is by no means limited in that respect. Instead'of preparing in advance the organic borate which is formed (I believe) by reaction of the boric acid and ethylene or di-ethylene glycol, for example, it is in' general more advantageous to produce the same in situ, soto speak, by incorporating the necessary reagents in the molding mixture; I may also use to advan- Example 4 Molding sand approximately 93 to 91 parts Organic borate approximately 3 to Sparta Naphthalene approximately. 4 liparts Water Suflicient Example 5 Molding sand 1 approximately 98 parts Boric acid approximately 211211128 Boric acid approximately lpa'rt Ethylene glycol, 40 per cent aqueone solution Sufllcient J Example 8- Molding sand approximately 9'3 parts Ammonium bisulfate approximately Zparts Naphthalene approximately 4parts Boric acid ap roximately lpart tage ammonium phosphate, the use of which 1s more fully described in the copending aplication of Francis C. Frary and myself,

erial No. 401,962, filed with.

Inthe following examples and in the appended claims the term sand is intended to include not only that particular material but similar inactive materials which, in commonly accepted molding practice, are used to form molds of the agglomerated ornonpermanent type. These examples (in which the parts stated are by weight) represent a number of molding compositions which have been found especially advantageous in casting the easily concurrently hereoxidizable metals and parti cularly magnesium and its alloys, according to the precepts of my invention. The water or other tempering medium is added in amount suflicient to give the desired molding consistency.

' Examples 1 and Molding sand approximately 93 to 97 parts Sulfur approximately 6 to 2parts' Boric aci approximately 1 lpart Di-ethylene glycol, 40 per cent aqueous solution"; Sufficient Sullicient Example 3 Molding sand approximately 94 parts Sulfur approximately 2 parts ,Anthracene approximately 3parts Boric acid approximately 1. part Di-ethyl'ene glycol, 40 per cent aqueous solution Ethylene glycol, 40 per cent aqueous solution Suiiicient Example 6 Molding sand approximately -95 parts Naphthalene-.. approximately iparts Boric acid approximately lpart Ethylene glycol, 40 per cent .aqu'eous solution Suiilcient Example 7 approximately 97 parts Molding sand approximately Zparts Ethylene glycol, 40 per cent aque-'.

one solution Example 9 Molding sand approximately 98 parts Boric acid approximately 2parts Ethylene glycol, 25 per cent aque- Suflicient one solution v Example 10.

approximately 93 parts approximately 4 parts approximately 2 parts approximately 1 part Suflicient Borlc acid Ethylene glycol, 60 per cent aqueous sol ion Example 11 approximately 97 parts approximately 2 parts approximately 1 part Molding sand Ammonium bisulfate- Boric acid Ethylene glycol, 25 per cent aqueone solution Snflicient Example 12. Molding sand approximately 90 to 88 parts Organic horate approximately 3 to 5parts Sulfur approximately 2 2parts Naphthalene approximately 3 1 3 parts Ammonium bisulfate approximately 2 2-parts Water Suflicient Example 13 Molding sand approximately 98 to 97 parts Borax (sodiumtetrabornte) Aqueous solution containing 15 per cent-sulfuric aci and 40 per cent ethylene glycol S ufllcient v v l u I; I It is to be understood that. my invention 1s not limited to the specific forms hereln described but can be carried out 1n other ways without departure from its sp1r1t. Invent1ons d1sclosed but not claimed herein are claimed 1n my four copendingappllcations Serial Nos. 401,957,401959, 401,960, 401,961,

and the aforesaid oin't application of Franapproximately 2 to 3 parts cis C. Frary and myself, Serial No. 401,962,

all filed of even date herewith.

. I claim 1. The method of casting easily oxidizable metals in sand molds, comprising mixing with the sand a plurality of protective substances of variant vaporizing temperatures,

including boric acid and di-ethyleneglycol,

4.. In a method of casting magnesium and other easily oxidizable metals in a sand mold,

producing in the moldaround the metal a plurality of 'dlfl'erent protective vapors including a vapor of an organic borate.

.5. In a methodof casting magnesmm and other easily oxidizable metals in sand molds,

producing in the mold around the metal a vapor of an organic borate.

6. The method of casting comprising mixing with the sand boric acid and an aqueous solution of a polyhydricalcomagnesium and other easilyoxidizable metals in sand molds,

hol, forming a mold of the mixture, and casting the metal in the mold.

The method of casting magnesium and other easily oxidizable metals in sand molds,

comprising mixing with the sand 1 to 2 per cent of boric acid and a suificient quantity of an aqueous solution of a polyhydric alcohol to lend good molding properties to the mixture, forming a mold of the mixture, and casting the metal in the mold.

8. Thamethod of casting other easily oxidizable metals, comp mixing with sand, boric acid and a 25 to 75 per cent aqueous solution of a polyhydric alcohol in amount sufiicient to give suitable molding properties, forming a mold of'the mixture, and'casting the metal in the mold.

9. The method of casting magnesium and other easily oxidizable metals, comprising mixing with sand boric acid and a 25 to 7 5 per cent aqueous solution of (ii-ethylene glycol, forming a mold of the mixture, and casting the metal in the mold.

V 10. The method of casting magnesium and other easily oxidizable metals in sand molds comprising mixing with sand a plurality oi protective substances of variant vaporizing temperatures, includin boric acid and a polyhydric alcohol, sul r and naphthalene; forming a mold of the mixture, and casting the metal in the mold.

11. A mold for casting magnesium and other easily oxidizable metals, made of a mixture containing sand and -an organic borate.

12. A mold for casting magnesium and other easily oxidizable metals, made of a mixture containing sand, boric acid and a polyhydric alcohol.

13. A mold for casting magnesium and other easily oxidizable metals made of a mixture containing sand, horic acidand diethylene glycol.

In testimony whereof I hereto aflix my signature. I

RQBERT THOMAS WOOD.

magnesium and 

